import math
x1,y1,x2,y2=map(float,input().split())
X=x2-x1
Y=y2-y1
L=math.sqrt(X**2+Y**2)
print(f'{L:.8f}')
 import math math x1,y1,x2,y2=map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 X=x2-x1 X x2-x1 x2 x1 Y=y2-y1 Y y2-y1 y2 y1 L=math.sqrt(X**2+Y**2) L math.sqrt(X**2+Y**2) math.sqrt math sqrt X**2+Y**2 X**2 X 2 Y**2 Y 2 print(f'{L:.8f}') print f'{L:.8f}' x2,y2=map(float,input().split()) map(float,input().split()) x2 X=x2-x1 x2-x1 X x1,y1,x2,y2=map(float,input().split()) map(float,input().split()) x1 y1,x2,y2=map(float,input().split()) map(float,input().split()) y1 y2=map(float,input().split()) map(float,input().split()) y2 Y=y2-y1 y2-y1 Y L=math.sqrt(X**2+Y**2) math.sqrt(X**2+Y**2) L
import math
x1,y1,x2,y2=map(float,input().split())
X=x2-x1
Y=y2-y1
L=math.sqrt(X**2+Y**2)
print(f'{L:.8f}')

